1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to a transfer voltage control method of an image forming apparatus.
2. Description of the Related Art
A conventional image forming apparatus of a transfer photographic method may include a feeding unit, an optical transfer apparatus, a developing unit, a transfer unit, a fixing unit, and a discharge unit.
A sheet of paper picked up from the feeding unit passes the developing unit, and the transfer unit, an image is printed on the sheet of paper, the image is fixed on a sheet of paper by the fixing unit, and the sheet of paper is discharged externally through the discharge unit.
Toner is pasted onto a latent image formed on a photoconductive medium, or a toner image is transferred from a photoconductive medium to a transfer unit or from a transfer unit to a sheet of paper using a difference in electrical potential of each apparatus. A proper transfer voltage has to be supplied to the transfer unit to transfer the toner image on the photoconductive medium onto the sheet of paper. A variation in resistance and an optimum transfer voltage are measured prior to printing. The optimum transfer voltage may be approximately +1200V to +1400V.
A color image forming apparatus may include a transfer unit including a first transfer member and a second transfer member to transfer an image using a plurality of colors. Recently, as demand for high speed color image forming apparatuses has increased, a first transfer member has been provided in a transfer drum to improve printing speed, and a structure in which uncontacted developer is used has been suggested.
A transfer unit including a plurality of transfer members has the problem that variation in the resistance of each transfer member cannot be accurately measured. For example, when the variation in the resistance of the first transfer member is measured, the variation in the resistance is measured according to a current variation by supplying a measurement voltage 500˜600V to the first transfer member. The voltage is also supplied to the second transfer member and the photoconductive medium contacting the first transfer member, and the variation in the resistance of the first transfer member is measured including the resistance values of the second transfer member and the photoconductive medium. As a result, the measured variation in resistance may be inaccurate. When a variation in current is measured by supplying a measurement voltage to the second transfer member to recognize a variation in the resistance of the second transfer member, errors of the measured variation in the resistance may be increased.
As an optimum transfer voltage is not set when the variation in the resistance of the first and second transfer members is not accurately measured, a method to alleviate transfer faults caused by errors of the transfer voltage, or image loss caused by overvoltage, is required.